Fuel filters such as fuel/water separators for internal combustion engines include a closed sheet metal vessel or shell which houses a filter element that is held and located within the shell by a coil spring. During typical operation, fuel flows through the filter element while water and heavier molecular particles are separated from the fuel and accumulate in a domed lower end portion of the shell. The water and other contaminants which accumulate as a result of the filtering process must be drained periodically from the shell. To this end, the domed end of the shell includes a port comprising a central aperture and a ferrule which is in the form of a metal ring with internal threads. A drain plug usually is threaded into the ferrule. Alternatively, a sensor with a selectively openable and closable drain valve may be threaded into the ferrule. The sensor is used to detect a variety of conditions within the filter.
In use, the filter is subjected to elevated pressures and thus the port must be designed to avoid leakage and to resist failure in a high pressure environment. Commercially available filters, which employ conventionally designed drain/fill/sensor ports, often experience severe performance limitations when repeatedly subjected to elevated pressures. Indeed, when subjected to testing, one presently commercially available filter housing burst at an average pressure of 230 psi and required replacement after only 53,000 test cycles.
The ports of conventional filters are often constructed by punching a hexagonal aperture through the center of the domed shell. A ferrule is then positioned within the aperture and is secured to the shell with an adhesive sealant such as Plastisol to complete the port. This design is less than optimal because the hexagonal central aperture, when subjected to high pressures, quickly develops fatigue cracking in its corners. In extreme cases, such fatigue cracking can eventually result in bursting since, during use, fuel is continually forced through the filter at high pressures and impose relatively high stress on the port.
Further, conventional port designs require two sealing points which often result in leakage problems in addition to the problems of bursting mentioned above. The first sealing point is disposed between the ferrule and the shell and is achieved by affixing the ferrule to the shell with the adhesive sealant. Such adhesives can eventually work loose, thereby opening gaps between the ferrule and the shell and often resulting in leakage. The second seal is typically an O-ring disposed between the ferrule and the drain plug or sensor. Since multiple seal arrangements create multiple paths for leakage, a filter incorporating such seals can develop leaks in a relatively short time.